This issue has been closed as 'Won't Fix' due to an extended period of time without updates. If this issue is important to you please let us know by posting on the AnswerHub or UDN, and Epic will re-open the ticket for further review.
When a player pawn overlaps a foliage/instanced mesh component, it triggers repeated begin/end overlap events on the foliage actor even when the player barely moves.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-26536 in the post.